This is where truly gulliblepeople are often referred when they self-deprecatingly refer to themselves as the sorts who believe the word gullible is not defined in the dictionary.
G: Yes, I am the guy who believes gullible is not in the dictionary.
M: But what about "gullible" spelled with 4 Ls? I.e., "gulllible." It's because of people like you that silly stuff like that actually gets added to the dictionary.
Someone who possesses the brain of a 12 year old girl, who has not gone through puberty or lack thereof any life skills for her to be equipped with the basic knowledge of life.